1. Field of the Invention
The present invention relates generally to ink-jet technology, more particularly to printheads for ink-jet pens, and, more specifically, to an ink-jet printhead with redundant nozzles and a method of use.
2. Description of the Related Art
The art of ink-jet technology is relatively well developed. Commercial products such as computer printers, graphics plotters, and facsimile machines, employ ink-jet technology for producing hard copy. The basics of this technology are disclosed, for example, in various articles in the Hewlett-Packard Journal, Vol. 36, No. 5 (May 1985), Vol. 39, No. 4 (August 1988), Vol. 39, No. 5 (October 1988), Vol. 43, No. 4 (August 1992), Vol. 43, No. 6 (December 1992) and Vol. 45, No.1 (February 1994) editions, incorporated herein by reference.
In ink-jet pen technology prior art, as generally depicted in FIGS. 1 and 2, it is known to provide a pen body 10 having an ink reservoir section 12 containing a supply of ink (not shown). The pen 10 includes a snout 25 with a printhead 14. The printhead 14 includes an orifice plate 18, having a nozzle array 16 with nozzles 17 aligned in combination with subjacent heating elements. Windows 22, 24 in the orifice plate 18 facilitate mounting of the printhead 14.
As depicted in FIG. 3, each nozzle region is a drop generator device which includes a heating element, resistor 304, a firing chamber 306 where nucleation and bubble growth takes place, and the nozzle 302 itself through which the ink droplet is fired at the medium.
In operation, ink is fed from the reservoir to the drop generators (ARROW A). The printhead 10 is coupled to printer control circuitry (not shown) by contact pads 20 of a flex circuit coupling the drop generators to the printer controls. Thermal excitation of ink (also sometimes referred to as dye or colorant) from the reservoir at the drop generators is used to eject droplets through the tiny nozzles 17 onto an adjacent print medium in a dot matrix configuration. The pen 10 is generally held in a carriage and scanned bidirectionally across the print medium, firing the ink droplets as it scans. The orifice array 16 is arranged to be selectively activated via the flex circuit 20 to fire simultaneously or in rapid succession during scanning to create a swath of small droplets on the medium in order to print characters or images.
The orifice plate and nozzle array configuration is one of the main ink-jet apparatus design factors that controls droplet size, velocity and trajectory of the droplets. In the state of the art, it is known to print one-third inch swaths at a six-hundred dot-per-inch ("DPI") density, making ink-jet capable of approaching electrophotographic quality. It is believed that 1200 DPI can be achieved with today's technology. This is accomplished in state of the art ink-jet printers by using thin film and semiconductor fabrication technologies to develop printheads with orifice arrays having over hundreds orifices with orifice spacing based upon the print density to be achieved. The larger the nozzle array, the more difficult the design challenges to ensure print quality.
As will be recognized by a person skilled in the art the present invention is applicable to a variety of other pen designs.
In order to accomplish high quality print results, different strategies can be employed for the deposition of ink droplets on the media. That is, print quality, particularly text, is improved by increasing the effective resolution of an image and selectively placing or deleting ink dots to improve the overall smoothness of the character.
Exemplary methods are discussed in U.S. Pat. No. 4,1663,882 (Hickman, commonly assigned to the assignee of the present invention) filed on Dec. 27, 1988, for Printing of Pixel Locations by an Ink Jet Printer Using Multiple Nozzles for Each Pixel or Pixel Row (incorporated herein by reference in its entirety). Dot-On-Dot ("DOD") and Double-Dot-Always ("DDA") techniques are disclosed for printing multiple ink dots on a single pixel from either the same nozzle, or from two different nozzles of a given array in order to compensate for improperly operating or inoperable nozzles. As stated beginning at col. 2, line 16: "In one strategy, each dot is formed from at least two droplets of each color, from different nozzles . . . . In another strategy, dots that require the same colors in a single pixel row are formed using droplets from different nozzles, so that the degradation in image quality due to a failed nozzle is significantly reduced." In other words, Hickman uses multiple combinations of nozzles of a standard array.
With increasing print speed and nozzle density, there is a continuing need for technology which will enhance ink-jet print quality.